Railway signaling system



R. R. KEMMERER RAILWAY SIGNALING SYSTEM June 15, 1943.

5 Sheets-Sheet 1 Filed March 15, 1941 Conlmlled by Zkafifiz'c c'HAdl/anee 31 ill-j T35 INVENTOR Ralph emmQPeP.

HIS ATTORNEY 5 Sheets-Sheet 2 Filed March 15, 1941 INVENTOR Ralph H. @1 91 HIS A'i'TORNEY June 15, 1943. R. R. KEMM ERER RAILWAY SIGNALING SYSTEM 5 Sheets-Sheet 5 Filed March 15, 1941 Signal Conz ol 20 C ouz'r. E422 '1; c 7

H l hRmvEN'roR ap 17212201 91. Fey. 6 BY HIS Ar'roRNEY June 15, 1943. R. R. KEMMERER 2 RAILWAY SIGNALING SYSTEM Filed March 15, 1941 5 Sheets-Sheet 4 INVENTOR [11s Ar'roRNEY 5 Sheets-Sheet 5 Filed March 15, 1941' Fig. 7.

Swz 6011 Looking INV TOR Ralph 12. 12201 91.

HIS ATTORNEY Patented June 15, 1943 RAILWAY SIGNALING SYSTEM Ralph E. Kcmmerer, Swissvale, Pa., as'signor to The Union Switch & Signal Company, Swissvale, Pa, a corporation of Pennsylvania Application March 15, 1941, Serial No. 383,571

12 Claims.

My invention relates to a railway signaling system and particularly to the provision of normally coded track circuits for detector purposes at interlockings.

It is an object of my invention to provide a detector track circuit employing coded energy to thereby secure the advantage of greater shunting sensitivity and increased protection against momentary loss of shunt which results from the use of coded instead of steady energy.

Another object of my invention is to provide a detector circuit of the type described in which on occupancy the supply of coded detector energy is out 01f while coded energy of suitable frequency selected in accordance with traffic conditions in advance is supplied to the section rails for cab signal control.

A further object of my invention is to provide a detector circuit of the type described which is arranged so that the most restrictive cab signal will be displayed if a locomotive overruns a wayside signal displaying its stop indication.

I shall describe several forms of railway signaling system embodying my invention,-and shall then point out the novel features thereof in claims.

In the drawings Fig. 1 is a diagram showing the system provided by this invention applied to a section of track in a track stretch through which trafiic normally moves in one direction only,

Fig. 2 is a diagram showing a system of the type shown in Fig. 1 applied to a section of track in a track stretch where trafiic normally moves in both directions,

Figs. 3 and 4 are diagrams showing modified systems applicable to sections where traific moves in one direction only,

Fig. 5 is a diagram showing a modified system applicable to sections where trafiic moves in both directions, and

Figs. 6 and 7 are diagrams showing modifications incorporating means to effect rapid reclearing of a signal following a momentary interruption in the supply of track circuit energy.

Similar reference characters refer to similar parts in each of the several views.

In Fig. 1 of the drawings there is shown a stretch of railroad track having a main track A and a siding or diverging track B which is connected with the main track by means of a track switch W.

The main track A has track rails l and 2 over which trafiic normally moves in the direction indicated by the arrow, that is from left to right.

The rails of the track A are divided by insulated joints 3 into track sections in the customary manner. The section including the track switch is designated 2T and is known as the detector section, while the adjacent sections in advance and in the rear are designated IT and. 3T.

A wayside signal S is provided and controls movement of trafiic on the main track over the track switch and also controls movement of traflic from the main track to the branch track. The wayside signal S is manually controlled in any manner well known in the art, while the control of this signal is interlocked with the control of the track switch. Except as hereinafter pointed out in detail the means for controlling the switch and the signal are not a part of this invention, and has been omitted from Fig. 1 of the drawings to simplify the disclosure.

The detector section 2T is supplied with alternating current of suitable frequency, such as cycles per second, which may be supplied from any suitable source the terminals of which are designated BX and CK.

The equipment is shown in the condition which it assumes when the track stretch is vacant. At this time coded alternating current of a suitable code frequency, such as 180 impulses per minute, is supplied to the rails of the detector section. The circuit for supplying this energy is traced from terminal BX through contact I of a continuously operating code transmitter ZCT, front contact Iii of relay CR, back contact ll of relay V and primary windingof track transformer TT. This energy is supplied over the track rails and through the transformer TU and rectifier RX to the winding of the relay TR, and also to the pickup winding of code detecting relay CR. which is connected in multiple with the track relay winding.

On the supply of an impulse of energy to the windings of these relays their contacts become picked up, while on termination of the impulse of energy the track relay contacts release.

The relay CR and the other parts of the equipment are selected and proportioned so that the energy supplied to the pick-up winding is effective to pick up the relay contacts but does not build up sufficient flux in the relay core to maintain the relay contacts picked up during the intervals between the supply of impulses of energy to this winding.

In order to maintain the contacts of relay CR steadily picked up as long as coded energy is supplied to the track relay and to the relay CR means is provided for supplying energy to the holding winding of the relay. As shown, the track relay contact 12 when picked up establishes a circuit to supply energy from a local source of direct current, the terminals of which are designated B and C, to one portion of the primary winding of the decoding transformer DT, while contact Id of the track relay establishes a circuit to supply energy from the transformer secondary winding to the holding windmg.

Accordingly, as long as the track relay responds to coded energy, an impulse of energy is supplied from the decoding transformer to the holding winding of the relay CR each time the track relay contacts are picked up. Thi energy assists the pick-up winding to maintain the relay contacts picked up, while it increases the flux density in the relay core to a sufiiciently high value that it is efiective to maintain the relay contacts picked up during the OE periods in the code.

A resistor I5 is connected across the terminals of the holding winding of relay CR to render the relay slow to release and to suppress the are at the track relay contact 14 on opening of this contact.

As relay CR is picked up, its contact [6 interrupts the circuit of the approach relay V, while its contact I! establishes the circuit of the relay P. As the relay P is energized, its contact I8 is closed and permits the circuit of the signal control relay SR to be established by the signal control lever L. The relay SR controls the signal S in such manner that the signal can be conditioned to display a proceed indication only when the relay SR is energized. As the circuit of the relay SR may be established at this time, the operator may condition the signal S to display a proceed indication to permit a train to move across the switch. On energization of the signal control relay SR its contact 20 is picked up and establishes a circuit to permit energy to be supplied to the relay V.

If after signal S has been conditioned to display a proceed indication a train'moving in the normal direction of traflic enters the detector section, it will shunt the track relay TR and the relay CR. On release of the track relay contacts the supply of energy to the holding winding of relay CR is cut ofi and the contacts of this relay quickly release so that contact l6 establishes the circuit of relay V, while contact IT interrupts the circuit of relay P. Relay P thereupon releases and its contact l8 interrupts the circuit of signal control relay SR so that the contacts of this relay release. The relay SR is of a type which is slow in releasing and its contact 20 remains picked up long enough after release of relay CR to insure that sufficient energy will be supplied to relay V to pick up the contacts of this relay. On picking up of the contacts of relay V its contact 2! establishes a stick circuit to maintain itself energized as long as relay CR i released.

On picking up of relay V its contact H interrupts the circuit for supplying coded energy from the code transmitter 2CT and establishes a circuit controlled by relays H and J for supplying energy to the track transformer TT. The relays H and J are governed by trafiic conditions in section 3'1 and in the adjacent section in advance so that the relay H is picked up when section 3T is vacant, while relay J is picked up only when section 3T and the adjacent section in advance thereof are both vacant.

As the track stretch is assumed to be vacant,

the relays H and J are both picked up so that on picking up of contact H of relay V energy of 180 code frequency is supplied to the track transformer TI and to the rails of section 2T. Accordingly the cab signal apparatus on the locomotive present in section 2T will operate to provide its green or clear indication, which is proper as the track stretch in advance is vacant.

If at the time the train enters the detector section section ET is vacant but the section in advance is occupied, relay H will be picked up but relay J will be released and energy of '75 code frequency will be supplied to the rails of section 2T so that the cab signal equipment will provide its yellow or caution indication. If at the time the train enters section 2T section ST is occupied, relay H will be released and steady energy will be supplied to the rails of section 2T so that the cab signal apparatus will operate to provide its most restrictive indication.

When the train advances into section ET, the track relay, not shown, for that section is shunted while relays H and J become released. As a result of release of relay H, the supply of coded energy to the transformer TT is cut 05 and steady energy is supplied thereto. When the train vacates section 2T, this steady energy feeds to the track relay TR and to the pick-up winding of relay CR and the contacts of these relays pick up. As steady energy is supplied to the pick-up winding of relay CR, the contacts of this relay are steadily picked up even though energy is not supplied to the holding winding of the relay after initial movement of the track relay contacts to their picked-up position.

On picking up of relay CR contact i6 interrupts the circuit of relay V, while contact IT establishes the circuit of relay P and contact it! establishes the circuit to supply energy of 180 code frequency from code transmitter 2C'I to track transformer TT on release of contact H of relay V.

On the change in the supply of energy to the rails of section 2T from steady to coded energy the track relay TR responds to coded energy so that impulses of energy are supplied to the hold ing Winding of relay CR to keep the contacts of this relay picked up during the off periods in the code.

As a result of the supply of energy to the relay P, the contact of this relay picks up and permits the circuit of the signal control relay SR to be established.

This system is arranged so that it provides rapid shunting on entrance of a train into the detector section. Since the detector section track relay is supplied with energy of 180 code frequency, the track relay follows this code and upplies impulses of energy through the decoding transformer DT to the holding winding of relay CR. As soon as the track relay is shunted, the supply of energy to the holding winding of relay GR is cut off and the contacts of this relay quickly release.

As energy of a relatively high code frequency is employed, the oil? periods in the code are relatively short, and the release time oi the relay CR need not be very long to bridge over these periods. Accordingly the relay will release very soon after the supply of energy to the relay is cut off. This prompt release of the relay CR is advantageous as it insures prompt initiation of the supply of cab signal control energy to the rails of the track circuit.

This system is also arranged so that an imperfect shunt or a shunt of relatively high resistance will cause release of the relay CR. Under such circumstances the energy which reaches the track relay TR and the pick-up winding of the relay CR will be very weak so that the track relay will not pick up at all, or if it picks up, its contacts will remain in their picked-up positions only for very brief periods 50 that very little energy is supplied from the secondary winding of transformer DT to the holding winding of relay CR. Accordingly, the relay CR will not pick up, or will pick up only for very short periods. When the contacts of relay CR are picked up, contact I? establishes the circuit to supply energy to relay P. The relay P, however, is of a type the contacts of which are slow to pick up and the relay contact does not pick up on this momentary energization of the relay winding. Accordingly contact l8 remains released and continues to interrupt the circuit of relay SR so that contact 23 of relay SR interrupts the pick-up circuit of relay V, while the relay SR also operates to prevent clearing of the signal S at this time.

The slow pick-up characteristic of relay P also serves to prevent picking up of its contact in the event of momentary loss of shunt which might occur when the section is occupied by a light Weight high speed vehicle.

The system provided by this invention is arranged so that if a train overruns the signal S at a time when the signal is displaying its stop indication, steady uncoded energy will be supplied. to the detector section rails to thereby cause the locomotive cab signal apparatus to display its most restrictive indication.

When the signal S is displaying its stop indication, the relay SR is released and its contact 2%) interrupts the pick-up circuit of relay V. Accordingly on entrance of a train into the detector section and release of relays TR and CR energy is not supplied to relay V so the contact H of this relay remains released and steady un-- coded energy is supplied to the track transformer TT over the circuit which includes back contact it! of relay CR and back contact ll of relay V.

Under these conditions, therefore, steady energy is supplied to the detector section rails and the cab signal apparatus will provide its most restrictive indication.

The coded detector circuit provided by this invention is applicable to locations in which traflic moves in both directions and Fig. 2 is a diagram showing this application of the invention.

The circuit shown in Fig. 2 is similar to that shown in Fig. 1 and employs the track relay TR and detector relay CR employed in the system shown in Fig. 1.

In the system shown in Fig. 2 a signal SE is provided to control eastbound traific and a signal SW is provided to control Westbound I traffic. These signals are governed by relays SRE and SRW in such manner that the signal SE will display 3, proceed indication when and only when relay SRE is picked up, and so that signal SW will display a proceed indication when and only when relay SRW is picked up. The relays SRE and SRW may be interlocked so that only one of these relays may be picked up at one time, while these relays may also be governed in accordance with the position of the switch W in the manner well known in the art. The control of the relays SRE and SRW is not a part of this invention and has been omitted to simpl fy the disclosure.

The equipment is shown in the condition which itassumes when the track stretch is vacant and the signals SE and SW are conditioned to display stop indications. At this time energy of 180 code frequency is supplied to coding relay CP over the circuit which is traced from terminal B through contact I of code transmitter 2CT, front contact H] of relay CR, back contact H of relay VE, back contact 25 of relay VW, and winding of relay GP to terminal C of the source of current.

On the supply of energy to the relay CP the contacts of this relay are picked up and contact 26 establishes a circuit to supply energy to the track transformer TTE at the right-hand end of the detector section, while contact 2'! establishes the circuit to supply energy from the rectifier RX to the track relay winding, and to the pick-up winding of relay CR. The circuit for supplying energy to track transformer TTE includes back contact 28 of relay VW, while the circuit for connecting transformer TU across the section rails includes the primary winding of transformer -TTW. At this time, however, the secondary winding of transformer TTW is short circuited by a circuit which includes back contact 39 of relay VW so that the impedance of the transformer primary winding is at the minimum and energy may flow freely from the track rails to transformer TU.

At this time, therefore, during the picked-up periods of relay CP energy is supplied to transformer TTE, and therefrom over the track rails to transformer TV, from which energy is supplied through the rectifier RX to relays TR and CR over the circuit established by contact 2'! of relay CP.

As a result of the supply of energy to the track relay TR its contacts pick up and an impulse of energy is supplied through decoding transformer DT to the holding winding of relay CR.

During the off periods in the code supplied to relay CP the contacts of this relay release and cut off the supply of energy to the track transformer and from the transformer TU to relays .TR and CR. As a result, the contacts of relay TR release, while as explained in connection with Fig. 1, the contacts of relay CR remain pi lied up. In addition, on release of the contacts of relay CP contact 21 short circuits the track relay winding and the pick-up winding of relay CR to insure release of the track relay, and also of the relay CR on expiration of its release period.

If the operator wishes to prepare the track for passage of an eastbound train, he may do so by establishing the circuit of relay SRE to thereby cause its contact 20 to pick up.

If an eastbound train now enters section 2T, the track relay TR and detector relay CR are shunted and contact 16 of relay CR establishes the pick-up circuit of relay VE, while contact Ill interrupts the circuit traced above for supplying coded energy to the relay CP. On the supply of energy to relay VE contact 2| establishes the stick circuit for the relay, while contact H establishes a circuit for supplying energy to relay CP. This circuit is controlled by relays HE and JE, which are governed by trafiic conditions to the east of section 2T as explained in connection with the corresponding relays in the system shown in Fig. 1. As the track stretch is assumed to be vacant, relays HE and JE are both picked up so that energy of code frequency is supplied to the relay CP over the circuit which includes contact l8!) of code transmitter 3CT.

Accordingly the contacts of relay CP are picked up and released at the 180 frequency and contact 26 establishes the circuit to supply energy to transformer TTE so that the cab signal apparatus on the locomotive operates to provide its green or clear indication.

At this time contact 21 of relay CP establishes the circuit for supplying energy to the track re lay and the pick-up winding of relay CR, but as a train is present in the detector section, energy is not supplied to these relays.

If at the time the train enters the detector section, section 3T is vacant but the section to the east thereof is occupied, relay HE will be picked up but relay JE will be released and energy of 75 code frequency will be supplied to relay CP so that energy of this code frequency will be supplied to the section rails and the locomotive cab signal equipment will provide its caution indication.

Similarly, if when the locomotive enters the detector section, section 3T is occupied, relay HE will be released and steady energy will be supplied to relay CP and as its contacts remain steadily picked up, steady energy will be supplied to the track circuit, and the locomotive cab signal apparatus will operate to provide its stop indication.

When the train advances far enough to enter section 31, the relay HE releases, if it is not already released, so that steady energy is supplied to the relay CP with the result that steady energy is supplied to the track transformer TTE, while contact 21 of relay CP establishes the circuit to permit energy to be supplied to relays TR and CR. When the train vacates section 2T, the steady energy supplied to the section rails feeds to transformer TU and is supplied therefrom to relays TR and CR so that the contacts of relay CR pick up, and contact l6 interrupts the circuit of relay VE. The contacts of this relay thereupon release and contact I l establishes the circuit for supplying energy of 180 code frequency from code transmitter 2CT to relay CP. Thereafter this relay operates to supply energy of 180 code frequency to transformer 'I'IE, and to permit energy to be supplied to the relays TR and CR so that the relay CR remains picked up.

The operation of the equipment on movement of a westbound train through the track stretch is similar to that for eastbound movements. When a westbound train is in the stretch, the operator will cause relay SRW to be energized to thereby permit signal SW to be conditioned to display a proceed indication. At this time relay SRE will be released.

When the westbound train enters section ET, the supply of energy over the track rails to the relays TR and CR is cut off and the contacts of relay CR release and establish the pick-up circuit of relay VW. This circuit includes front contact 32 of relay SRW, and back contact 33 of relay CR, while contact 34 of relay VW when picked up establishes a stick circuit for the relay.

On picking up of the contacts of relay VW contact 25 interrupts the circuit for supplying energy from code transmitter 2CT to relay CP and establishes a circuit governed by trafiic conditions in the west of section 2T for supplying energy to relay CP. This circuit is governed by relays HW and JW which are controlled in substantially the same manner as relays HE and J E.

If at this time the track stretch is vacant, relays JW and HW will both be picked up and energy of code frequency will be supplied to relay CP from code transmitter lCT.

On picking up of relay VW its contact 30 interrupts the circuit short circuiting the primary winding of transformer TTW, and establishes a circuit to permit energy to be supplied to the transformer I'IW during the released periods of contact 26 of relay CP, and to cause the primary winding of transformer 'IIW to be short circuited by contact 36 of relay CP durin the picked-up periods of this contact.

The circuit for supplying energy to the trans former TTW is traced from terminal BX through back contact 26 of relay CP, and front contact 30 of relay VW to one terminal of the transformer primary winding, while the other terminal of this winding is connected to terminal CX of the source of current. During th picked-up periods of relay CP the supply of energy to-the transformer TTW is cut off, while the primary winding of this transformer is short circuited by a circuit which is traced from one terminal of the winding through front contact 36 of relay CP and front contact 30 of relay VW to the other terminal of the winding.

It will be seen that on entrance of a westbound train into the detector section ener y is supplied to the section rails at the exit end of the section, and that the type of energy supplied is selected in accordance with traflfic conditions in advance. Accordingly the locomotive cab signal apparatus will operate to provide the appropriate signal indication.

At this time, that is when a westbound train is present in the detector section, steady energy is supplied to transformer T'I'E over the circuit which includes front contact 28 of relay VW. However, the train prevents this energy from reaching the exit end of the detector section.

It will be seen also that energy is supplied to the transformer TTW during the released periods of relay CP and that at these times contact 21 of relay CP not only interrupts the circuit for supplying energy from rectifier RX to relay TR and CR, but also short circuits the windings of these relays. During the picked-up periods of relay CP contact 2! establishes the circuit from rectifier RX to relays TR and CR, but at this time contact 36 short circuits the primary winding of transformer TTW so that no energy can be supplied to the detector section track circuit, and hence cannot be supplied to relays TR and CR. Accordingly when the detector section is conditioned for westbound traific, the relays TR and CR both remain released.

When the westbound train enters section IT, relay HW releases so that steady energy is supplied to relay CP and its contacts remain picked up so that energy is no longer supplied to transformer TTW, while contact 21 establishes the circuits of the relays TR and CR.

When the westbound train vacates section 2T, the steady energy supplied to transformer TTE feeds to transformer TU and therefrom through rectifier RX to relays TR and CR so that the contacts of these relays pick up. On picking up of contact 33 of relay CR the circuit of relay VW is interrupted and the contacts of this relay release so that contact 30 short circuits transformer TTW, while contact 25 interrupts the supply of steady energy to relay CP and establishes the circuit including front contact l0 and back contact ll of relay VE for supplying energy of 180 code frequency to the relay CP. In addition, at this time contact 28 establishes the circuit including front contact 26 of relay GP for supplying coded energy to the transformer TTE. Thereafter impulses of energy are supplied to the track circuit during the picked-up periods of relay CP, while energy is supplied from the rectifier RX to the relays TR and CR at these times so that the relay TR follows code, while the relay CR remains picked up as explained in detail above.

The systems shown in Figs. 1 and 2 operate so that if 'the code transmitter 2CT should become defective and cease to operate at a time when its contact I80 is closed, steady uncoded energy would be supplied to the track circuit. This energy would be supplied to the track relay and to the pick-up winding of the relay CR and the contacts of the relay CR would be maintained picked up to maintain the supply of steady energy to the track circuit. Under this condition the advantage of high shunting sensitivity which results from the use of coded energy in the detector track section is lost. While the possibility of such a failure of the code transmitter is quite remote, it may be preferred to arrange the system so that such a failure will produce a safe condition, and Fig. 3 is a diagram of such a modification of the system shown in Fig. 1.

In the system shown in Fig. 1 the relay P is energized by current supplied over a circuit which includes front contact I! of relay CR so that if steady energy keeps the relay CR picked up, the relay P will be energized and its contact. l8 will be picked up so that signal relay SR may be energized to condition signal S to display a proceed indication.

In the modification shown in Fig. 3 the relay P is replaced by a relay PR which is energized through the decoding transformer DT so as to be energized only when the relay TR is responding to coded energy.

The system shown in Fig. 3 has a decoding transformer DT which is provided with two secondary windings, while energy is supplied from one of these windings to the holding winding of relay CR as explained in connection with Fig. 1. In the system shown in Fig. 3 the transformer DT has another secondary winding from which energy is supplied to relay PR on movement of the contact 38 of relay TR to its picked-up position, provided contact 4!! of relay CR is picked up.

The relay PR, like its counterpart relay P in the system shown in Fig. 1, is of a type the contacts of which are slow to pick up but quick to release. The relay PR has a contact 4| which controls the circuit of signal control relay SR,

Under normal conditions, when the detector section is vacant and coded energy is supplied to the section rails, the track relay TR responds to coded energy, while energy is supplied from the rectifier RX to the pick-up winding of relay CR. In addition, during the picked-up periods of the track relay contacts, energy is supplied to the holding winding of relay CR and to the winding of relay PR. Accordingly the contacts of relays CR and PR are picked up, and as contact M of relay PR is picked up, energy may be supplied to relay SR to condition signal S to display a proceed indication.

If, as stated above, the code transmitter 2CT should fail with its contact closed, steady energy will be supplied to the transformer TT and thus to the relays TR and CR. Suiiicient energy may be supplied to the pick-up winding of relay CR,

to maintain the contacts of this relay picked up. However, as the contacts of relay TR remain steadily picked up, energy is not supplied to the relay PR through the transformer DT and the contacts of relay PR release so that the circuit of relay SR is interrupted and cannot be established. Accordingly the signal S will be conditioned to provide its most restrictive indication and trains will be prevented from entering the detector section except at very low speeds so that the presence of steady energy instead of coded energy in the detector section track circuit will not produce a hazardous condition.

The modification shown in Fig. 3 otherwise 0perates in the same manner as the system shown in Fig. 1 and a detailed description thereof is not necessary.

In Fig. 4 of the drawings there is shown another systcm which may be employed to provide coded energy in the detector section track circuit to detect entrance of a train into the section and to thereafter cut off the detector code energy and supply to the section rails coded cab signal energy selected in accordance with trafdc conditions in advance.

The system shown in Fig. 4 is similar to that shown in Fig. 1, and differs therefrom in that a relay DR having a single winding is employed instead of the two winding relay CR, while a relay Q is added to control the circuit for supplying steady energy to the detector section track circuit. The relay DR is supplied with energy from the secondary winding of the decoding transformer DT and is proportioned so that the relay contacts will become picked up on the supply of a single impulse of energy from the transformer. The relay Q is energized by current supplied over a circuit which includes back contact 62 of track relay TR. The relay Q is of a type which is slow to release and on interruption of the supply of energy to the relay winding its contacts remain picked up for a period slightly longer than the longest off period in the coded energy supplied to the detector section track circuit.

The equipment is shown in the condition which it assumes when the detector section is vacant. At this time coded energy is supplied from code transmitter 2CT over front contact E0 of relay DR and back contact H of relay V to the track transformer TT. This energy is supplied over the track rails to track relay TR and during the picked-up periods of the track relay contacts energy is supplied from the secondary winding of transformer DT to relay DR, while during the released periods of the track relay energy is supplied to relay Q over the back contact 42 of the track relay. As long as the track relay responds to coded energy, therefore, relays DR and Q are both picked up.

When a train enters the detector section, the track relay TB, is shunted and its contacts remain released so that energy is not supplied to relay DR, and its contacts release. As the contact 42 of the track relay is released, energy is supplied to relay Q and its contact is picked up.

As a result of release of the contacts of relay DR, contact l6 establishes the pick-up circuit of relay V providing the contact 26 of relay SR. is picked up. If relay V picks up, its contact 2i establishes a stick circuit for the relay, while its contact I l establishes the circuit for supplying to the transformer TT energy coded or steady energy selected in accordance with traffic conditions in advance as explained in connection with interrupt the pick-up circuit of relay V so that on release of relay DR the relay V remains released. Under these circumstances steady energy is supplied to the track transformer 'IT from terminal BX through front contact 45 of relay Q, back contact I!) of relay DR, and back contact ll of relay V.

On release of relay DR. its contact I! interrupts the circuit of relay P so that its contact If; releases and interrupts the circuit of relay SR.

Under conditions of poor shunting sufiicient energy may be supplied to the track relay TR to pick up the contacts of this relay, but they will pick up so slowly that insufiicient energy is supplied from the transformer secondary winding to the relay DR to pick up the contacts of this relay. As steady energy is supplied to the track relay, its contacts remain steadily picked up and contact 42 interrupts the circuit of the relay Q, and

after a time interval its contact 45 releases and interrupts the supply of steady energy to the track transformer. Accordingly the track relay releases and reestablishes the circuit of relay Q, while contact 45 of relay Q picks up and again establishes the circuit for supplying steady energy to the track transformer.

If the unusual shunting condition continues, the track relay will again slowly pick up, while relay Q will again release and interrupt the supply of energy to the track circuit. Even if this cycle is repeated indefinitely, a dangerous condi tion is not created as it has been found that the impulses of energy supplied to the track circuit under these conditions are too short and occur too infrequently to cause operation of locomotive cab signal apparatus. In addition, under these conditions relay P is released and interrupts the circuit of the signal control relay SR so that signal S displays its stop indication and cannot be caused to provide a proceed indication. The relay P may also control circuits, not shown, for locking the switch W to prevent movement of the switch when the relay P is released.

The modification shown in Fig. 4 is designed for use in sections where trafiic normally moves in one direction only. The system shown therein is adapted for use in sections in which trafilc moves in both directions, however, and Fig. 5

is a diagram of this form of the invention The system shown in Fig. 5 is that shown in Fig. 2 modified in the same manner as the system shown in Fig. 4.

The modification shown in Fig. 5 employs a relay DR. having a single winding which is supplied with energy from the decoding transformer DT when the track relay contacts are in their picked-up positions. This modification also employs the relay Q which is energized over a circuit which includes back contact 42 of the track relay, while contact 45 of the relay Q controls the circuit for supplying steady energy to the relay CP.

Under normal conditions the operation of the system shown in Fig. 5 is substantially the same as that of the system shown in Fig. 2 and a detailed explanation thereof is unnecessary The system shown in Fig. 5 operates in substantially the same manner as that shown in Fig. 4 in the event the unusual shunting condition exists when the detector section is occupied and steady energy is supplied to the detector section over the circuit which includes contact 45 of relay Q. Steady energy is supplied in this manner in the event that a train overruns a signal displaying a stop indication. For purposes of illustration it will be assumed that signal SE is displaying a stop indication, and that an eastbound train runs past the signal SE.

When the signal SE is displaying a stop indication, signal control relay SRE is released and its contact 20 interrupts the pick-up circuit of relay VE. Accordingly on shunting of the track relay TR and release of relay DR relay VE remains released and steady energy is supplied to relay CP over the circuit which includes front contact 45 of relay Q, back contact H] of relay DR, back contact ll of relay VE, and back contact 25 of relay VW. The contacts of relay CP, therefore, are steadily picked up and steady energy is supplied to track transformer TTE over the circuit which includes front contact 25 of relay CP, and back contact 28 of relay VW.

Under unusual shunting conditions, as explained in connection with Fig. 4, sumcient energy may be supplied through the transformer TU, rectifier RX, and front contact 21 of relay 0? to the track relay TR to slowly pick up the contacts of this relay. If this occurs, too little energy will be supplied from the decoding transformer to relay DR to pick up the contacts of this relay, while as the track relay contacts are picked up contact 42 interrupts the circuit of relay Q so that contact 45 of relay Q interrupts the supply of steady energy to relay CP. Thereupon the contacts of relay CP release and contact 25 interrupts the supply of steady energy to the transformer TTE, while contact 21 interrupts the supply of energy from the track rails to the relay TR and establishes a circuit shunting the track relay winding. Accordingly the track relay TR releases and its contact 42 establishes the circuit to supply energy to relay Q so that its contact 45 picks up and reestablishes the circuit to supply steady energy to relay CP. The contacts of relay CP, therefore, pick up and steady energy is again supplied to transformer 'ITE, while contact 2'! again establishes the circuit to permit energy to be supplied from the section rails to relay TR.

If the unusual shunting condition continues, the track relay will again slowly pick up so that relay Q will again release and interrupt the supply of steady energy to relay CP so that it re leases and interrupts the supply of energy to the track transformer TTE. As pointed out in connection with the system shown in Fig. 4, a dangerous condition will not be produced even if this cycle is repeated continuously.

The system shown in Fig. 1 may be modified so as to include means effective in the event of failure of the source of alternating current at a time when the signal S is displaying a proceed indication to condition the signal to display its stop indication, and thereafter on restoration of the source of alternating current to permit the signal to again display its proceed indication without operation of the signal lever or release of the locking for the signal and the associated switch.

Fig. 6 is a fragmentary diagram showing the system of Fig. l modified to incorporate the means described above. In the system shown in Fig. 6 a power-off relay PO is provided which is energized from the same source of alternating current as that from which energy is supplied to the detector section track circuit. The power-ofi relay PO is normally energized by current supplied over a stick circuit which includes its own front contact 50.

In the system shown in Fig. 6 the slow pickup relay P is provided with a stick circuit which includes its own front contact while it is provided with a pick-up circuit which includes back contact 53 of relay P0. The relay P is provided with another pick-up circuit which is governed by an approach relay AR which is controlled in the manner well known in the art by trafiic conditions in th track stretch approaching the signal so that the relay AR is picked up and establishes the pick-up circuit for the relay P only when this stretch is vacant. The relay P has a contact l8 which controls the signal control relay SR and a contact 55 which controls the pickup circuit of the power-off relay PO.

Under normal conditions with the detector section vacant the relay CR is picked up and energy is supplied to relay P over front contact I! of relay CR and front contact 5| of relay P, while the relay PO is energized by current supplied over both its pick-upand stick circuits.

At this time contact it of relay P is picked up and permits the operator to establish the circuit of the relay SR to clear the signal controlled thereby.

For purposes of illustration it will be assumed that the operator moves the signal control lever L to the position to energize relay SR, that a train enters the approach section leading to the signal so that the approach locking is effective, and that there is a momentary failure of the source of alternating current.

As a result of this failure of the source of alternating current, energy ceases to be supplied to the track circuit of the detector section so that the track relay ceases to follow code while relay CR releases and its contact I! interrupts the circuit of relay P. Relay P thereupon releases and its contact 18 interrupts the circuit of relay SR so that relay SR releases and places the associated signal at stop.

On release of relay P its contact 55 interrupts the stick circuit for the relay, but at this time the power-off relay PO also releases because of the failure of the source of alternating current and its contact 53 establishes a pick-up circuit for relay P. In addition, contact 50 of relay PO interrupts the stick circuit for the relay, while the pick-up circuit for the relay PO is interrupted by contact 55 of relay P.

On subsequent restoration of the source of alternating current energy is again supplied to the track circuit and relay CR picks up and its contact I1 completes the pick-up circuit of relay P. As soon as relay P picks up, its contact 5| establishes a stick circuit to maintain itself energized, while contact 55 establishes the pick-up circuit of the power-off relay PO. On picking up of relay P its contact I5 completes the circuit of relay SR, assuming that signal control lever L remains in the position to which it had been moved, and relay SR picks up so that the signal controlled thereby is again conditioned to provide its proceed indication.

Interruptions in the supply of alternating current are usually only of momentary duration and may be caused by transfer from one substation to another. The system provided by this modification of the invention is advantageous as it permits the signal to clear after such a momentary interruption and thus permits a train approaching the signal to proceed without unnecessary delay. If this means were not provided, and there were a momentary interruption in the source, th signal would be placed at stop and pix could not be made to display a proceed indication without waiting for the release of the time delay controlled locking means, not shown.

While the control means shown in Fig. 6 has been illustrated and described in connection with the system shown in Fig. 1, this means is equally applicable to the system shown in Fig. 4.

The system shown in Fig. 3 may be modified to incorporate means effective on restoration of the supply of alternating current following an interruption to permit the signal to again display a proceed indication, and Fig. '7 is a diagram showing this modification.

The modification shown in Fig. 7 is the same as that shown in Fig. 3 except for the addition of the power-off relay PO, the approach locking relay AR, and for changes in the circuit of the relay PR.

The power-ofi relay PO is energized from the source of alternating current from which energy is supplied to the detector section track circuit. The relay P0 has a pick-up circuit which includes front contact (ill of relay PR, and a stick circuit which includes its own front contact Bi. The approach locking relay AR is governed in the manner well known in the art by trafiic conditions in the track stretch approaching the signal and is energized only when this stretch is vacant. The relay PR is provided with pick-up circuits one of which includes back contact (52 of relay PO, and the other of which includes front contact 63 of relay AR, while the relay PR is provided with a stick circuit which includes its own front contact 64.

Under normal conditions the modification shown in Fig. 7 operates in substantially the same manner as that shown in Fig. 3 and a de tailed explanation of its operation is unnecessary.

If the operator wishes to clear the signal S, he may do so by moving the lever L to the position shown. This will establish the circuit of the signal control relay SR, assuming that the detector section is vacant and that relay PR is icked up.

When a train enters the approach section, ra lay AR releases and interrupts one pick-up Gin. cuit for the relay PR.

If while the train is in the approach section there is a failure of the source of alternating current, energy will not be supplied to the detector section track circuit and relay TR will cease to follow code so that relays PR and CR release. On release of relay PR its contact 4i interrupts the circuit of relay SR so that this relay releases and causes the signal S to display its stop indication.

In addition, on interruption of the supply of alternating current energy the power-oif relay PO releases and its contact 6| interrupts the stick circuit for the relay, while its contact 52 establishes a pick-up circuit for the relay PR.

On release of the relay CR at a time when the relay SR is picked up the pick-up circuit for relay V is established by contact lfi of relay CR so that relay V picks up and its contact 2| establishes a stick circuit for the relay. According- 1y contact H of relay V is picked up and establishes the circuit for supplying coded energy to transformer TT according to tramc conditions in advance, and on subsequent restoration of the supply of alternating current energy is supplied to the detector section track circuit over this circuit.

The energy supplied to the detector section track circuit feeds to relay TR and to the pickup winding of relay CR so that relay CR picks up and its contact l6 interrupts the circuit of relay V and its contact l establishes the circuit for supplying coded energy from the code transmitter 2CT to the track transformer TI on release of contact ll of relay V. On thi supply of coded energy to the track circuit the track relay TR responds to coded energy so that impulses of energy are supplied from a secondary winding of the transformer DT to the relay PR over the pick-up circuit which is traced from one terminal of th transformer secondary winding through front contact 38 of relay TR, back contact 62 of relay PO, front contact 40 of relay CR, and winding of relay PR to the other terminal of the transformer secondary winding. Accordingly relay PR picks up and its contact 64 establishes a stick circuit to maintain itself energized as long as the track relay responds to coded energy. In addition, on picking up of relay PR contact 60 establishes the pick-up circuit of the power-off relay PO so that its contact 62 interrupts the pick-up circuit of relay PR, while contact 6| of relay PO establishes a stick circuit to maintain the relay energized. On picking up of the relay PR its contact 4| establishes th circuit of relay SR so that this relay picks up and again conditions the signal S to provide a proceed indication.

From the foregoing it will be seen that each of the modifications of the invention provides means operative when a track section is vacant to supply coded detector energy to the track circuit for the track section, and operative on entrance of a train into the section to out 01f the supply of coded detector energy and to supply at the exit end of the section coded cab signal control energy selected in accordance with traffic conditions in advance.

In addition, it will be seen that the systems shown in Figs. 2 and 5 are adapted for use where traffic moves in both directions, and operate to supply cab signal control energy at the exit end of the section regardless of the direction of movement of the train which enters the system.

It will be seen also that the modifications shown in Figs. 6 and '7 provide means to permit rapid reclearing of a signal on restoration of the supply of alternating current following an interruption in such supply.

Although I have herein shown and described only several forms of railway signaling system embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is: I

1. In a coded railway signaling system, in combination, a stretch of railway track having a pair of track rails divided by insulated joints into a plurality of track sections including a detector section, a signal governing entrance of trains into said detector section, a signal control relay operative only when energized to permit said signal to display a proceed indication, electroresponsive means governed by energy supplied over the rails of said detector section, and means governed by said electroresponsive means and said signal control relay for supplying energy to the detector section rails, said means being effective when said electroresponsive means is energized to supply coded energy to the detector section rails and being effective on deenergization of said electroresponsive means when said signal control relay is released to supply steady energy to the detector section rails, said means being efiective on deenergization of said electroresponsive means when said signal control relay is energized to supply to the detector section rails coded or steady energy selected in accordance with traflic conditions in the adjacent section in advance of said detector section.

2. In a coded railway signaling system, in combination, a section of railroad track having a pair of track rails over which traffic moves in both directions, the rails of said track stretch being divided by insulated joints into a plurality of track sections including a detector section which is adjoined on one side by a first section and on the other side by a second section, a first signal governing movement of trains from the first section into said detector section and a second signal governing movement of trains from the second section into said detector section, a first control relay associated with said first signal and a second control relay associated with said second signal, each control relay being effective only when energized to permit the associated signal to provide a proceed indication, electroresponsive means governed by energy supplied over the rails of said detector section, and means controlled by said electroresponsive means and by said signal control relays for supplying energy to the rails of said detector section, said means being effective when said electroresponsive means is energized to supply coded energy to the detector section rails and on deenergization of said electroresponsive means when the signal control relays are deenergized to supply steady energy to the rails of said detector section, said means being effective on deenergization of said electroresponsive means when the first signal control relay is energized to supply to the rails of said detector section steady or codedenergy selected in accordance with traffic conditions in said second section, and being effective on deenergization of said electroresponsive means when said second signal control relay is energized to supply to the rails of said detector section steady or coded energy selected in accordance with trafic conditions in said first section.

3. In a coded railway signaling system, in combination, a section of railroad track having a pair of track rails over which traffic moves in both directions, the rails of said track stretch being divided by insulated joints into the plurality of track sections including a detector section which is adjoined on one side by a first section and on the other side by a second section, a first signal governing movement of trains from the first section into said detector section and a second signal governing movement of trains from the second section into said detector section, a first control relay associated with said first signal and a second control relay associated with said second signal, each control relay being effective only when energized to permit the associated signal to provide a proceed indication, electroresponsive means located at the end of the detector section adjacent said first section and governed by energy supplied over the rails of said detector section, and means controlled by said electroresponsive means and by said signal control relays. for supplying energy to the rails of said detector section, said means being effective when said electroresponsive means is energized to supply coded. energy to the detector section rails at the end of the detector section adjacent said second section and on deenergization of the electroresponsive means when the signal control relays are deenergized to supply steady energy to the rails of said detector section at the end of the detector section adjacent said section, said means being effective on deenergization of said electroresponsive means when the first signal control relay is energized to supply to the detector section rails at the end of the section adjacent said second section steady or coded energy selected in accordance with traffic conditions in said second section, and being effective on deenergization of said electroresponsive means when the second signal control relay is energized to supply to the detector section rails at the end of the section adjacent said first section steady or coded energy selected in accordance with trafiic conditions in said first section. I

4. In a coded railway signaling system, in combination, a section of railroad track having a pair of track rails over which traffic moves in both directions, the rails of said track stretch bein divided by insulated joints into a plurality of track sections including a detector section which is adjoined on one side by a first section and on the other side by a second section, a first signal governing movement of trains from the first section into said detector section and a second signal governing movement of trains from the second section into said detector section, a first control relay associated with said first signal and a second control relay associated with said second signal, each control relay being effective only when energized to permit the associated signal to provide a proceed indication, a coding relay, electroresponsive means located at the end of the detector section adjacent said first section, a circuit including a front contact of said coding relay for supplying energy from the detector section rails to said electroresponsive means, means governed by said electroresponsive means and by said first and second signal control relays for supplying energy to said coding relay, said means being effective when said electroresponsive means is energized to supply coded energy to said coding relay, said means being effective on deenergization of the electroresponsive means when the first signal control relay is energized to supply to the coding relay coded or steady energy selected in accordance with trafiic conditions in said second section and being effective on deenergization of said electroresponsive means when the second signal control relay is energized to supply to the coding relay coded or steady energy selected in accordance with trafiic conditions in said first section, means effective when the second signal control relay is released to establish a circuit including a front contact of said coding relay for supplying energy to the detector section rails at the end of the detector section adjacent said second section, and means eifective when the second signal control relay is picked up to establish a circuit including a back contact of said coding relay for supplying energy to the detector section rails at the end of the detector section adjacent said first section.

5. In a coded railway signaling system, in combination, a stretch of railway track having a pair of track rails divided by insulated joints into a plurality of track sections including a detector section, a signal governing entrance of trains into said detector section, a signal control relay operative only when energized to permit said signal to display a proceed indication, electroresponsive means controlled by energy supplied over the rails of said detector section, means governed by said electroresponsive means and elfective to permit the circuit of the signal control relay to be established only when said electroresponsive means is energized, a circuit complete when said electroresponsive means is energized for supplying codded energy to the rails of said detector Section, a circuit complete on deenergization of said electroresponsive means when the signal control relay is released for supplying steady energy to the rails of said detector section, and means effective on deenergization of said electroresponsive means when said signal control relay is energized to establish a circuit to supply to the detector section rails steady or coded energy selected in accordance with trailio conditions in the adjacent section in advance of said detector section.

6. In a coded railway signaling system, in combination, a stretch of railway track having a pair of track rails divided by insulated joints into a plurality of track sections including a detector section, a signal governing entrance of trains into said detector section, a signal control relay operative only when energized to permit said sig nal to display a proceed indication, electroresponsive means governed by energy supplied over the rails of said detector section, an auxiliary relay elfective when picked up to permitthe circuit of the signal control relay to be established and to establish a stick circuit to maintain itself energized, a source of track circuit energy, a power-off relay energized from said source and effective when deenergized to permit a pick-up circuit for said auxiliary relay to be established, said electroresponsive means governing the pickup and stick circuits for said auxiliary relay and being effective only when energized to permit said circuits to be established, and means govsignal control relay for supplying energy from said source of current to the detector section rails, said means being effective when said electroresponsive means is energized to supply coded en- 'ergy to the rails of said detector section and being eifective on deenergization of said electroresponsive means when the signal control relay is released to supply steady energy to the rails of said I detector section, said means being also effective on deenergization of said electroresponsive means at a time when said signal control relay is energized to supply steady or coded energy to the rails of said detector section depending upon traflic conditions in the adjacent section in advance of said detector section.

7. In a coded railway signaling system, in combination, a stretch of railway track having apair of track rails divided by insulated joints into a plurality of track sections including a" detector section, a signal governing entrance of trains into said detector section, a signal control relay operative only when energized to permit the signal to display a proceed indication, electroresponsivemeans governed by energy supplied over the rails of said detector section, an auxiliary relay effective only when energized to permit the circuit of the signal control relay to be established, means effective only when coded energy is supplied to said electroresponsive means for supp y energy to said auxiliary relay, and means governed by said electroresponsive means and said signal control relay for supplying energy to the detector section rails, said means being effectivewhen said electroresponsive means is energized to supply coded energy to the detector section rails and being effective on deenergization of said electroresponsive means when said signal control relay is released to supply steady energy to the detector section, said means being efiective on deenergization of said electroresponsive means when said signal control relay is picked up to supply to the detector section rails steady or coded energy selected in accordance with trafiic conditions in the adjacent section in advance of said detector section.

8. In a coded railway signaling system, in combination, a stretch of railway track having a pair of track rails divided by insulated joints into a plurality of track sections including a detector section, a signal governing entrance of trains into said detector section, a signal control relay operative only when energized to permit said signal to display a proceed indication, a code following track relay receiving energy over the detector section rails, a code detecting relay and an auxiliary relay associated with said track relay, means effective only when the track relay is supplied with coded energy to supply energy to said code detecting relay, a circuit including a back contact of the track relay for supplying energy to said auxiliary relay, and means governed by said code detecting relay and said signal control relay for supplying energy to the detector section rails, said means being effective when said code detecting relay is energized to supply coded energy to the detector section rails and being efi'ective on release of said code de- I tecting relay when the signal control relay is released to establish a circuit including a front contact of said auxiliary relay for supplying steady energy to the detector section rails, said means being efiective on release of the code detecting relay when the signal control relayis picked up to supply to the detector section rails steady or coded energy selected in accordance with traffice conditions in the adjacent section in advance of said detector section.

9. In a coded railway signaling system, in

combination, a stretch of railway track having a pair of track rails divided by insulated joints into a plurality of track sections including a detector section, a signal governing entrance of trains into said detector section, a signal control relay operative only when energized to permit said si nal to display a proceed indication, a code following track relay and an auxiliary relay each having a winding receiving energy over the detector section rails. a transformer, a circuit including a contact of said track relay for supplying direct current to the transformer primary the signal control relay is released to supply steady energy to the detector section rails, said means being eifective on release of the auxiliary relay when the signal control relay is picked up to supply to the detector section rails steady or coded energy selected in accordance with traffic conditions in the adjacent section in advance of said detector section.

10. In a coded railway signaling system, in combination, a stretch of railway track having a pair of track rails divided by insulated joints into a plurality of track sections including a detector section, a signal governing entrance of trains into said detector section, a slow release signal control relay operative only when energized to permit said signal to display a proceed indication, electroresponsive means governed by energy supplied over the detector section rails, a circuit controlled by said means and eifective only when said means is energized to permit energy to be supplied to said signal control relay, a governing relay having a pick-up circuit complete when said electroresponsive means is deenergized and the signal control relay is energized and a stick circuit complete when said electroresponsive means is deenergized and said governing relay is picked up, a circuit effective when said electroresponsive means is energized to supply coded energy to the detector section rails, a circuit efiective when the electroresponsive means is deenergized and said governing relay is released to supply steady energy to said detector section rails, and a circuit effective when said governing relay is picked up to supply to the detector section rails steady or coded energy selected in accordance with trafiic conditions in the adjacent section in advance of said detector section.

11. In a coded railway signaling system, in combination, a section of railroad track having a pair of track rails over which traiiic moves in both directions, the rails of said track stretch being divided by insulated joints into a plurality of track sections including a detector section which is adjoined on one side by a first section and on the other side by a second section, a first signal governing movement of trains from the first section into the detector section and a second signal governing movement of trains from the second section into said detector section, a first winding and a circuit including a front contact of said track relay for sup lying energy from the transformer secondary winding to a winding of said aux liary relay. the energy supplied from the transformer to the auxiliary relay being effective to maintain the auxiliary relay picked up during the intervals between the impulses of coded energy supplied to the auxiliary relay over the detector section rails, and means controlled by sa d auxiliary relay and the si nal control relay for supplying energy to the detector section rails, said means being effective when said auxiliary relay is picked up to supply coded encrew to the detector section rails and being effective on release of said auxiliary relay when control relay associated with said first signal and a second control relay associated with said second signal, each control relay being efi'ective only when energized to permit the associated signal to provide a proceed indication, electroresponsive means governed by energy supplied over the detector section rails, a first governing relay having a pick-up circuit complete when the electroresponsive means is deenergized and the first signal control relay is picked up, a second governing relay having a pick-up circuit complete when the electroresponsive means is deenergized and the second signal control relay is picked up, each of said governing relays having a stick circuit complete when said relay is picked up and the electroresponsive means is deenergized, and means controlled by said electroresponsive means and by said governing relays for supplying energy to the detector section rails, said means bein efi'ective when said electroresponsive means iv energized to supply coded energy to the detector section rails and being efiective when said. electroresponsive means is deenergized and the governing relays are both released to supply steady energy to the detector section rails, said means being effective when the first governing relay is picked up to supply to the detector section rails steady or coded energy selected in accordance with trafiic conditions in said second section and being effective when the second governing relay is picked up to supply to the detector section rails steady or coded energy selected in accordance with traific conditions in said first section.

12. In a coded railway signaling system, in combination, a stretch of railway track having a pair of track rails divided by insulated joints into a plurality of track sections including a detector section, a signal governing entrance of trains into said detector section, a signal control relay operative only when energized to permit said signal to display a proceed indication, electroresponsive means governed by energy supplied over the detector section rails, a governing relay having a pick-up circuit complete when said signal control relay is picked up and said electroresponsive means is deenergized and having a stick circuit complete when said electroresponsive means is deenergized and said governing relay is picked up, a circuit effective when said electroresponsive means is energized to supply coded energy to the detector section rails, a circuit effective when the electroresponsive means is deenergized and the governing relay is released to supply steady energy to the detector section rails, and a circuit effective when the governing relay is picked up to supply to the detector section rails steady or coded energy selected in accordance with traffic conditions in the adjacent section in advance of said detector section.

RALPH R. KEMMERER. 

